Visitor pattern

src/behavioral/SConscript

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+#
+# This file is part of cpp-patterns.
+#
+# cpp-patterns is free software: you can redistribute it and/or modify
+# it under the terms of the GNU General Public License as published by
+# the Free Software Foundation, either version 3 of the License, or
+# (at your option) any later version.
+#
+# cpp-patterns is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with cpp-patterns.  If not, see <http://www.gnu.org/licenses/>.
+#
+
+Import('env')
+
+env.program(targetName='visitorEx',
+            sources=['visitor/visitor.cpp'],
+            localSharedLibs=[])

src/behavioral/visitor/IElement.hpp

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+/*
+ * This file is part of cpp-patterns.
+ *
+ * cpp-patterns is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * cpp-patterns is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with cpp-patterns.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+#ifndef SRC_BEHAVIORAL_VISITOR_IELEMENT_HPP_
+#define SRC_BEHAVIORAL_VISITOR_IELEMENT_HPP_
+
+#include "IVisitor.hpp"
+
+namespace behavioral {
+
+namespace visitor {
+
+struct IElement {
+  virtual ~IElement() = default;
+
+  virtual void accept(IVisitor& visitor) = 0;
+};
+
+}  // namespace visitor
+
+}  // namespace behavioral
+
+#endif  // SRC_BEHAVIORAL_VISITOR_IELEMENT_HPP_

src/behavioral/visitor/IVisitor.hpp

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+/*
+ * This file is part of cpp-patterns.
+ *
+ * cpp-patterns is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * cpp-patterns is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with cpp-patterns.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+#ifndef SRC_BEHAVIORAL_VISITOR_IVISITOR_HPP_
+#define SRC_BEHAVIORAL_VISITOR_IVISITOR_HPP_
+
+class ElementA;
+class ElementB;
+
+namespace behavioral {
+
+namespace visitor {
+
+struct IVisitor {
+  virtual ~IVisitor() = default;
+
+  virtual void visit(ElementA& element) = 0;
+  virtual void visit(ElementB& element) = 0;
+};
+
+}  // namespace visitor
+
+}  // namespace behavioral
+
+#endif  // SRC_BEHAVIORAL_VISITOR_IVISITOR_HPP_

src/behavioral/visitor/visitor.cpp

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+/*
+ * This file is part of cpp-patterns.
+ *
+ * cpp-patterns is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * cpp-patterns is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with cpp-patterns.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+#include "IElement.hpp"
+#include "IVisitor.hpp"
+
+#include <algorithm>
+#include <iostream>
+#include <memory>
+#include <vector>
+
+struct ElementA : public behavioral::visitor::IElement {
+  virtual void accept(behavioral::visitor::IVisitor& visitor) override
+  {
+    std::cout << "ElementA::accept\n";
+    visitor.visit(*this);
+  }
+};
+
+struct ElementB : public behavioral::visitor::IElement {
+  virtual void accept(behavioral::visitor::IVisitor& visitor) override
+  {
+    std::cout << "ElementB:accept\n";
+    visitor.visit(*this);
+  }
+};
+
+struct VisitorA : public behavioral::visitor::IVisitor {
+  virtual void visit(ElementA& element) override
+  {
+    std::cout << "VisitorA::visit(ElementA)\n";
+  }
+
+  virtual void visit(ElementB& element) override
+  {
+    std::cout << "VisitorA::visit(ElementB)\n";
+  }
+};
+
+int
+main(int argc, char** argv)
+{
+  VisitorA va;
+
+  std::vector<std::unique_ptr<behavioral::visitor::IElement>> a(3);
+
+  a[0].reset(new ElementA());
+  a[1].reset(new ElementB());
+  a[2].reset(new ElementA());
+
+  std::for_each(a.begin(), a.end(), [&va](const auto& e) { e->accept(va); });
+}